Tight regulation of the cellular Fe(II) pool is imperative to prevent the accumulation of harmful byproducts. The Ferric Uptake Regulation (Fur) repressor protein from Escherichia coli is part of the iron homeostatic system and functions to repress transcription of Fe(II)-scavenging machinery under conditions of iron abundance. With the support of this fellowship, fundamental knowledge of how this system functions may be gathered which can then be applied to regulatory systems for iron and other metal ions in higher organisms. Proposed work will address both the selectivity and the sensitivity of Fur for Fe(II) relative to other metal ions. A battery of spectroscopic methods will be used to identify the coordination environments of the metal ions. The DNA-binding properties of the complex will be tested, and the potential of Fe(II)-Fur to act as a highly responsive metal sensor will be assessed. The protein/DNA contacts will be mapped and identified. Finally, the role of Fe(II) in the mechanism of transcriptional repression will be addressed.